Why not simulate that environment exactly?
For example, let's say you have a number of problems for them to solve during the interview process. Before you get to these problems, show the candidate something like the following:
Explain, as you did in your question, that the company makes thousands of dollars on a given project per hour. Thus, when there is a bug in the project which causes it to go down for an extended period of time, there is the potential for a great amount of profit loss. Furthermore, while some people may thrive in this type of environment, others would find it too stressful. Thus, in order to find out how they deal with this type of stressful situation, there is a portion of the interview process dedicated to replicating this environment to see how they will deal with it.
At this point, ask them if they are OK with this type of test. If not, then skip it and just ask the programming questions as normal and judge them on the rest of the interview, taking into account that they avoided the stressful situation. If so, click the "New Problem" button. Explain to them that a bug was found and the product is now down, and that in an actual situation, the clock would be running even while they are trying to figure out what the problem is. Also, explain that even though there is a time-crunch, fixing the bug properly is the bigger goal here. Then hand them the problem, preferably on a piece of paper with no further explanation and sit back, observe, and answer questions for them as you deem appropriate.
When they are finished with the problem, click the "Problem Fixed" button and evaluate their solution to make sure it meets the requirements. If it does not, click the "10-Minute Penalty" button, explaining again that fixing the bug properly is the bigger goal, and have them continue working as the Dollars Lost continues accruing.
Repeat for the remaining problems, asking them if they are ok to continue before starting the next problem, and possibly asking them how they are dealing with the stress of the situation. Be empathetic, understanding that this is not a fun process to go through (for most).
At the end you will get a concrete number for total dollars lost on all problems, as well as the qualitative experience of how they perform under pressure.
Here's the editable link for the simulation if you want to tweak it to better match your case.